Precision coaxial connector



Feb 17, 1970.

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w e N INVENTORS OTTMAR JQFIEBEL l BYFRANKLIN D.ROSEN o. J. FIEIBEL ET L Filed March 21, 1966 ATTORNEYS I United States Patent 3,496,496 PRECISION COAXIAL CONNECTOR Ottmar J. Fiebel, Holliston, and Franklin D. Rosen, Brighton, Mass., assignors to General RF Fittings, Inc., Boston, Mass.

Filed Mar. 21, 1966, Ser. No. 535,768 Int. Cl. H03h 7/38 U.S. Cl. 33333 11 Claims ABSTRACT OF THE DISCLOSURE A transmission line connection characterized by a low standing wave ratio has a reduced outer conductor diameter in the region of inner conductor overlap. In other sections the insulating spacers between the inner and outer conductors are cut away to provide partial air dielectrics compensating for different outer conductor diameters.

This invention relates to a connector for coaxial transmission lines. More particularly, it provides a radio frequency coaxial connector having a new transmission line structure that markedly reduces impedance discontinuities encountered in prior coaxial connectors of the same type. Due to this new structure, the connector can easily provide, on a production basis, superior impedance characteristics as were heretofore approached only in costly hand-finished connectors.

The invention is concerned primarily with connectors in which both the inner conductors and the outer conductors of the mating connector portions telescope together. This is in contrast to connections wherein the outer conductors meet in a face-to-face relation and have flanges that are bolted together to secure the connection.

Coaxial connectors are conventional devices-in common use since at least the 1940sused to interconnect radio frequency devices such as antennas, receivers, transmitters and test equipment having coaxial transmission line ports.

The principal function of a coaxial connector is reliably to conduct signals between the interconnected transmission lines without introducing a transmission discontinuity. That is, unless the connector is required to provide an impedance transformation, it should have precisely the same electrical impedance throughout its entire length as the two interconnected transmission lines, which generally have the same impedance. When the characteristic impedance at any point in the connector differs from that of the interconnected coaxial lines, the impedance discontinuity reflects part of the signal directed to the connector back to its source, i.e., to the input transmission line. This produces in the input line a voltage standing wave whose amplitude varies along the transmission line. The standing wave ratio (SWR) of the maximum voltage in the standing wave to the minimum voltage is a measure of the impedance discontinuity: the larger the discontinuity, the larger the SWR.

It is known in the art to compensate connectors to reduce the effect of impedance discontinuities. Thus, when a connector manufacturer measures an SWR in a connector that he has designed to have as few discontinuities as reasonably possible, he can introduce additional discontinuities to cancel the effects of the discontinuities that persist. This technique can reduce the SWR of the connector. However, compensation seldom provides a completely reflection-free connector. And the compensation is generally frequency sensitive so that the connector is well matched only over a limited frequency range.

Prior to the present invention, the current laboratory standard coaxial connectors were hand-finished and hand- 3,496,496 Patented Feb. 17, 1970 compensated with the plug and jack sections specially impedance-matched to each other. These prior precision connectors have a maximum SWR generally under 1.04 at frequencies up to 9 gHz. As might be expected, they are relatively high cost connectors, being roughly 7 to 10 times more expensive than standard connectors, which have a typical SWR of 1.3 over a similar frequency range.

Accordingly, it is an object of this invention to provide a coaxial transmission line connector that can be readily manufactured to have a low standing wave ratio. A further object is to provide such a connector for manufacture with a lower SWR than heretofore available except with hand-finishing for impedance improvement. It is also an object that the connector have such a low SWR over a relatively wide range of frequencies, preferably exceeding a 10:1 range. Another object of the invention is to provide such a precision connector at a relatively low cost, particularly at a cost competitive with previously available, standard connectors from relatively high volume manufacture.

A further object of the invention is to provide a coaxial transmission line connector having a precise, low SWR without requiring impedance compensation.

A more particular object is to improve the impedance characteristics, as manufactured, of types HN, BNC, C, SC, TNC, and like connectors without detracting from their mechanical and other electrical features.

A further object of the invention is to provide connectors of the above character whose jacks and plugs are separately compatible with prior art plugs and jacks, respectively.

It is also an object of the invention to provide a coaxial transmission line connector of the type in which the inner conductor receptacle of the jack has axiallyextending fingers that receive and frictionally engage the inner conductor pin of the plug, which connector has fewer impedance mismatches than its prior art counterpart.

Other objects of the invention will in part be obvious and will in part appear hereinafter.

The invention accordingly comprises the features of construction, combination of elements, and arrangement of parts which will be exemplified in the construction hereinafter set forth, and the scope of the invention will be indicated in the claims.

For a fuller understanding of the nature and objects of the invention, reference should be had to the following detailed description taken in connection with the accompanying drawings, in which:

FIGURE 1 is a side sectional View of a disengaged connector embodying the invention;

FIGURE 2 is a side view, partly broken away, of the assembled connector; and

FIGURE 3 is a transverse sectional view of the assembled connector as seen along line 3-3- in FIGURE 2.

In the prior art there are many standard coaxial connector designs. Also, in the highly competitive and rapidly developing microwave industry, many assertedly new connectors are continually being announced. The new connectors claim such improvements as smaller size, compatability with new cables, lower SWR, higher breakdown voltage, lower cost and higher reliability and versatility. However, this aggressive and competitive industry has been unaware that a common connector construction introduces impedance mismatches that can be removed in a relatively simple manner.

The sources of these mismatches have now been recognized and understood to such an extent that theoretical calculations result directly-without the experimental cutand-try refinements so commonly required to perfect microwave devices in almost perfect connectors. The invention thus provides structural changes in existing connectors that improve considerably their SWR, without hand tailoring. The new precision connectors are compatible with prior connectors and are no more costly to manufacture.

Specifically, it is now recognized that the common jack inner conductor receptacle having narrow slots to form axially-extending contact fingers has a measurably smaller effective radius, for impedance purposes, than an unslotted conductor of the same outer diameter. Further, it has been established that a reduction in the inner radius of the outer conductor opposite the slotted receptacle essentially completely offsets the impedance changes the slots would otherwise introduce. In one preferred embodiment then, the invention provides a connector with a conventional slotted inner conductor receptacle, and having a reduction in the outer conductor diameter opposite the slotted inner conductor.

The connector also has other departures from prior art, as will now be described in detail.

As shown in FIGURE 1, the connector comprises a plug indicated generally at and a jack indicated at 12. The illustrated jack is identical in many respects to a conventional TNC jack and has a slotted and bored inner conductor receptacle 14 and an outer conductor 16. An insulating sleeve 18 supports the receptacle within the outer conductor. The back end of the inner conductor receptacle 14 is connected to the inner conductor 24 of a coaxial transmission line 20. The transmission line outer conductor 22 is joined to the back end of the connector outer conductor 16. (The back ends of elements in the jack are their axial ends nearest where the transmission line extends from the jack; their other axial ends are referred to as their front ends. The elements of the plug 10 are similarly referred to as having back and front ends.)

The connector plug 10 has a cylindrical outer conductor 32 and an insulating sleeve 34 coaxially within the outer conductor and supporting an inner conductor pin 36. The inner conductor 44 of a coaxial line extends from the back end of the pin 36, and the transmission line outer conductor connects to the plug outer conductor 32.

Referring to FIGURES 1 and 2, the connector is assembled by threading a captive nut 48 axially retained on the plug 10 on threads 50 on the outside of the jack outer conductor 16, as is conventional. This urges the lug and jack together with the plug outer conductor 32 telescoping under the outer conductor 16 of the jack until the front face 52 of the plug outer conductor butts against the shoulder 54 on the jack outer conductor. At the same time, the inner conductor pin 36 of the plug fits in the bore within the fingers 56 of the jack inner conductor receptacle 14. The front edges of the fingers frictionally engage the pin forming a secure contact.

Referring again to FIGURE 1 and the construction of the jack 12, the jack inner conductor receptacle 14, disposed snugly within a bore in the insulating sleeve 18, has an unslotted cylindrical portion 14a behind the fingers 56. However, it has a uniform maximum outer diameter over its entire length when assembled with the plug pin 36. Further, the bases of the slots 57 are forward of the outer conductor shoulder 54 by a short but finite dis tance.

The jack has a normal transmission line section 58 the back limit of which is the bottom of a counterbore 59 in the insulating sleeve 18 and the forward end of which is the back edge of a retaining rim 60 on the outer conductor 16. The normal section is thus axially coextensive with the greater part of the unslotted cylindrical portion 14a of the receptacle 14. Forward of the normal section 58, for the short axial length of the outer conductor retaining rim 60, the jack has a retaining section 62 the forward limit of which is the shoulder 54. This section 62 is preferably also opposite only the unslotted receptacle portion 14a. Between the shoulder 54 and the front face of the outer conductor 16, which is the front edge of the jack, the jack has an overlapping section 64.

Along the length of the normal section 58 of the jack 12, the outer surface of the sleeve 18 firmly engages the outer conductor 16. The cylindrical inner surface of the outer con-ductor has a uniform diameter such that the transmission line characteristic impedance between the outer conductor and the receptacle portion 14a has a selected design value.

At the forward end of the jack normal section 58, the inwardly protruding retaining rim 60 on the outer conductor engages the insulating sleeve 18 to hold the sleeve and other elements of the jack in place, as is conventional. However, the reduced radial spacing between the outer conductor rim and the inner conductor receptacle tends to decrease the characteristic impedance in the section 62 below the design value in the normal section 58. This change in impedance would introduce an impedance discontinuity that would measurably increase the input SWR of the jack.

However, the present connector maintains the characteristic impedance in the retaining section 62 at the same value as in the normal section 58 by reducing the sleeve outer diameter to provide an air gap 66 beneath the rim 60. This partial replacement of the insulating sleeve by air increases the impedance in the retaining section of the jack to the design value. This is because air has a smaller permittivity than the material of the insulating sleeve 18, which may be of polytetrafiuoroethylne (commercially available under the trade designation of Teflon).

With further reference to FIGURE 1, in the overlapping section 64 of the jack, the outer conductor 16 is radially enlarged and the outer diameter of the insulating sleeve 18 is greatly reduced, compared to their dimensions in the sections 58 and 62, to provide a cylindrical gap that receives the front portion of the plug outer conductor and insulating sleeve, as shown in FIGURE 2. The shoulder 54 in the jack against which the plug outer conductor butts is at the back end of the overlapping section. Also in this section 64, the insulating sleeve 18 preferably extends forward just beyond the end of the slotted receptacle 14 to protect the fingers 56 from damage.

In the plug 10, the inner conductor pin 36 has a cylindrical portion 360 behind a tapered portion 36b; the diameter at the base of the tapered portion is less than the diameter of the cylindrical portion by twice the thickness of the jack receptacle fingers 56. The outer diameter of the cylindrical portion 36a is usually equal to the outer diameter of the cylindrical portion 14a of the jack receptacle 14.

With further reference to FIGURE 1, the connector plug has a normal transmission line section 68 the back end of which is the bottom of a counterbore 69 in the insulating sleeve 34 and the forward end of which is defined by the forward end of the pin cylindrical portion 36a.

Forward of this normal section 68, there is a slotted section 70 that is substantially coextensive with the tapered portion 36b of the pin 36. More particularly, as shown in FIGURE 2, the slotted section 70 is coextensive with the slots 57 in the jack inner conductor receptacle 14 when the connector is assembled.

Forward of the slotted section of the plug is an end section 72 where the outer conductor 32 extends beyond the inner conductor pin 36 and, in the assembled connector, extends into the jack for the axial distance from the base of the slots 57 to the jack outer conductor shoulder 54.

In the normal section 68 of the connector plug, the pin outer diameter and the outer conductor inner diameter are usually selected to provide the same design impedance as in the jack normal section 58 and hence have the same values as the corresponding diameters of the jack receptacle 14 and outer conductor 16. The inner conductor sleeve 34 snugly fits between these coaxial conductors in the section 68.

Considering the end section 72 of the plug 10, in the assembled connector, it is opposite the cylindrical portion 14a of the jack receptacle 14. Accordingly, to provide the same characteristic impedance as in the adjoining jack sections 58 and 62 (which have the same inner conductor diameter as the plug end section in the asssembled connector), the inner diameter of the plug outer conductor 32 would be expected to be identical to one of the outer conductor diameters in these jack sections 58 and 62. However, this is not the case, as will now be discussed.

In assembling the plug, the insulating sleeve 34 and the outer conductor 32 are slid onto each other and therefore the sleeve cannot have a larger outer diameter in the region of the end section 72 than it has in the region of the slotted section 70. It has therefore been determined that the sleeve 34 not extend forward beyond the slotted section 70; other arrangements can be employed, but this one is preferred for mechanical and electrical reasons. This leaves an air gap 74 in the assembled connector radially between the plug outer conductor 32 and the jack insulating sleeve 18. The net permittivity of the resultant combination of sleeve 18 and the air gap 74 between the assembled coaxial conductors in the plug end section 72 is generally different from the permittivity elsewhere in the connector. Accordingly, to provide the design value of characteristic impedance, the inner diameter of the plug outer conductor in the section 72 generally has a value different from the outer conductor diameters in the other sections of the connector. Specifically, because the illustrated air gap 74 is thicker than the air gap 66 in the section 62 of the jack 12, the inner diameter of the illustrated plug outer conductor in the section 72 is smaller than the outer conductor diameters in the connector sections 58, 62 or 68.

In the slotted section 70 of the plug, the inner diameter of the insulating sleeve 34 is enlarged to provide a cylindrical space for receiving the front part of the jack inner conductor receptacle and insulating sleeve with a minimal air space 76 (FIGURE 3) radially between the two assembled sleeves 18 and 34. This step in the inner diameter of the insulating sleeve 34 is preferably radially in-line wtih the forward end of the cylindrical portion 36:: of the inner conductor pin 36.

Further, the inner diameter of the outer conductor 32, which is a circumferentially-continuous cylinder, is measurably smaller in the slotted section 70 than in the normal section 68. For the reason now to be explained, this reduced outer conductor diameter in the slotted section 70 provides the same characteristic impedance, when the plug is assembled with the jack, as the larger, usually equal, outer conductor diameters in the plug normal section 68 and in the jack normal section 58.

In the assembled connector, FIGURE 2, the inner conductor portion opposite the outer conductor in the plug section 70 is the slotted portion of the jack receptacle 14. Due to the slots 57, the effective outer diameter for impedance purposes of this portion of the receptacle is less than the physical outer diameter thereof. When the reduced diameter in the slots, which as shown in FIG- URE 3 is the diameter at the base of the tapered section 36b of the plug inner conductor pin, is taken into account, the effective radius, r of the connector inner conductor in the plug section 70 can be shown to have the following value where:

r is the largest radius of the pin tapered portion 36b;

and l is the width of each of the slots 57. Equation 1 neglects second and higher order effects; however they are relatively small.

The inner radius, R, of the plug outer conductor 32 in the section 70 is determined for the design characteristic impedance, Z from the conventional equation using as the inner conductor radius r the value of r determined in accordance with Eq. 1. The permittivity e in Eq. 2 is the effective value determined according to conventional techniques from the permittivities of the sleeves 18 and 34 and of the gas in the narrow cylindrical space 76 (FIGURE 3) between the overlapping sleeves. Where the two sleeves have the same permittivity s and the gas in this space has a permittivity e (a for use in Eq. 2, can generally be calculated with sufficient accuracy as follows:

2 d netf 1 2 m) where: d is the thickness of the cylindrical space 76; and x is the radius to the middle of the space 76.

The effect of the permittivity in the slots 57 is usually so small that it can be neglected, and hence omitted from Eq. 3.

Substituting Eq. 1 into Eq. 2 provides the following expression for the value of the inner radius R of the plug outer conductor 32 in the section 70.

The radii thus calculated from the approximated Eqs. 1-4 have been found to be within /1% of the optimum values as determined by actual test.

The foregoing connector construction provides a marked reduction in SWR as contrasted with conventional prior connectors. In fact, a conventional TNC connector, for example, has the same outer conductor diameter opposite the slotted inner conductor as it has opposite the unslotted inner conductor. The resultant impedance discontinuity between the slotted and unslotted sections typically introduces a maximum SWR close to 1.1. Further, the prior TNC connector does not have the gaps 66 and 74 provided in the present construction and it lacks a section equivalent to the present plug end section 72. Moreover, the outer conductor of the conventional TNC plug, corresponding to the present conductor 32, has contact fingers that engage the inner surface of the jack outer conductor; it does not have the butt connection of the present connector between the plug outer conductor face 52 and the jack shoulder 54. As a result of this construction, the maximum SWR of the complete standard TNC connector is at least as high as 1.2 between 1 gHz. and 10 gI-Iz. The SWR of the improved construction described above, on the other hand, is generally below 1.03 over this 10:1 frequency range, and does not exceed 1.05. Indeed, connectors constructed in accordance with the invention often do not manifest a measurable standing wave. That is, any signal reflected from impedance discontinuities in the connector are too small to be distinguished from the noise in the measuring system.

The present connector construction provides this remarkable impedance match-with only conventional manufacturing techniques whereby all connectors are substantially alike. They do not require hand-finishing, tailored to each connector, as required in the prior art to attain equivalent impedance characteristics. As a result, the present connectors can readily be manufactured at the same cost as the conventional prior connectors of the same type.

It will thus be seen that the objects set forth above, among those made apparent from the preceding description, are efficiently attained and, since certain changes may be made in the above construction without departing from the scope of the invention, it is intended that all matter contained in the above description or shown in the accompanying drawing shall be interpreted as illustrative and not in a limiting sense.

It is also to be understood that the following claims are intended to cover all of the generic and specific features of the invention herein described, and all statements of the scope of the invention which, as a matter of language, might be said to fall therebetween.

Having described the invention, what is claimed as new and secure by Letters Patent is:

1. A coaxial transmission line connector for mating with another connector to provide a connection having a substantially constant characteristic impedance, said connector having (i) an outer conductor (22) and an insulating sleeve (ii) first, second and third contiguous axially consecutive sections with said second section being closer to the front end of the connector than said first end and said third end being closer to said front end than said second end, and

(iii) an inner conductor-receiving central bore extending through said insulating sleeve in said sections,

said connector being characterized in that (A) in said first section (58) 1) said outer conductor has a first inner diameter, and

(2) the outer surface of said insulating sleeve adjoins said outer conductor,

(B) in said second section (62) (1) said outer conductor has a second inner diameter smaller than said first diameter to form an inwardly protruding retaining rim (60) engaged with a radial surface of said insulating sleeve,

(2) a second insulating material having a smaller permittivity than the material of said insulating sleeve extends for a sufficient part of the radial distance between said outer conductor rim and said bore of said sleeve to provide substantially the same characteristic, impedance in said second section as in said first section, and

(1) said outer conduct-or has a third inner diameter larger than said second diameter thereof, and

( 2) said insulating sleeve has a fourth outer diameter considerably smaller than said second diameter thereby forming a cylindrical space between said outer conductor and said insulating sleeve for receiving the outer conductor of a mating connector.

2. A connector according to claim 1 further comprising an inner conductor receptacle (14) disposed in said bore coaxial with said outer conductor and having a portion (140) axially extending along said first and second sections, said receptacle portion having a substantially continuous cylindrical outer surface of uniform diameter in said first and second sections,

3. A coaxial transmission line connector jack having a front end at which it receives a mating connector plug and a back end axially removed therefrom, said jack comprising (A) a cylindrical inner conductor receptacle having a first outer diameter and being axially slotted, from its end closest to said front end of said jack, for a portion of its length to form a plurality of axiallyextending, pin-receiving, contact fingers,

(B) a cylindrical insulating sleeve (1) having a central axial bore in which said receptacle is disposed,

(2) having a first axial section that is at least partially coextensive with said slots in said receptacle and that has a second outer diameter,

(3) having a second axial section that is contiguous with the end of said first section nearest said back end of the jack and that has a third outer diameter larger than said second diameter, and

(4) having a third axial section that is contiguous with the end of said second section nearest the back end of the jack and that has a fourth outer diameter larger than said third diameter, and

(C) an outer conductor (1) having a cylindrical inner surface at least axially coextensive with first, second and third sections of said insulating sleeve,

(2) having a fifth axial section that is exactly coextensive with said second axial section of said cylindrical sleeve and that has a sixth inner diameter greater than said third diameter of said sleeve so that there is a gap radially between said sleeve and said outer conductor,

( 3) having a fourth axial section that is contiguous with the end of said fifth section nearest said front end of the jack and that has a seventh inner diameter larger than said sixth diameter thereof, and

(4) having a sixth axial section contiguous with the end of said fifth section nearest the back end of the jack and having an inner diameter substantially equal to said fourth diameter of insulating sleeve.

4. A coaxial transmission line connector for connection with a mating connector, said connectors being arranged to couple transmission lines having the same characteristic impedance, said transmission line connector being arranged for a low standing wave ratio and having (i) an outer conductor (48) coaxial and at least partly coextensive with an inner conductor (36) and with an insulating sleeve (34) between said conductors,

(ii) first and second contiguous axially consecutive sections (68, with said second section (70) being closer to the front end thereof that connects with a mating connector, and

(iii) a central bore extending through said insulating sleeve in both said sections,

a said connector being characterized in that (A) in said first section I 1) said inner conductor has a cylindrical part (36a) with a first outer diameter,

(2) the inner diameter of said outer conductor has a second value, and

(3) the inner diameter of said sleeve is substantially equal to said first diameter and the outer diameter of said sleeve is substantially equal to said second value, and

(B) in said second section (1) said inner conductor has a connecting part (36b) joined to said cylindrical part, said connecting part being arranged to fit within an inner conductor receptacle in said mating connector, said receptacle being slotted in the axial direction to form a plurality of fingers that fit over and frictionally engage said connecting part (2) the inner diameter of said outer conductor has a third value less than said second value, said third value being substantially twice the radius R determined from the following equation r is the radius to the outer surface of a finger of said receptacle when assembled with said connecting part where:

r is substantially equal to r,, less the radial thickness of said fingers at said slot;

1 is the width of the slots between adjacent fingers of said receptacle;

Z is the design characteristic impedance in said second section of said connector when assembled with said further mating connector; and

6 is the net permittivity of the insulating material between said outer conductor and said receptacle when said connectors are assembled together; and

(3) the outer diameter of said sleeve is substantially equal to said third value.

5. A coaxial transmission line connector for connection with a mating connector, said connectors being arranged to couple transmission lines having the same characteristic impedance, said transmission line connector being arranged for a low standing wave ratio and having (i) an outer conductor (48) coaxial and at least partly coextensive with an inner conductor (36) and with an insulating sleeve (34) between said conductors,

(ii) first, second and third contiguous axially consecutive sections (68, 70, 72) with said third section (72) being closest to the front end of said connector that connects with said mating connector, and said second section (70) being between said first and third sections, and

(iii) a central bore extending through said insulating sleeve in all said sections,

said connector being characterized in that (A) in said first section (1) said inner conductor has a cylindrical part (36a) with a first outer diameter,

(2) the inner diameter of said outer conductor has a second value, and

(3) the inner diameter of said sleeve is substantially equal to said first diameter and the outer diameter of said sleeve is substantially equal to said second value, and

(B) in said second section (1) said inner conductor has a connecting part (36b) joined to said cylindrical part,

(2) the inner diameter of said outer conductor has a third value less than said second diameter, and

(3) the outer diameter of said sleeve is substantially equal to said third value,

(C) in said third section said outer conductor has a fourth inner diameter greater than said third inner diameter value, and

(D) said insulating sleeve terminates at the end of said second section contiguous with said third section so as not to extend into said third section.

6. A conductor according to claim 5 in which said fourth outer conductor diameter is intermediate said sec- 0nd and third outer conductor diameters.

7. A connection between two coaxial transmission lines, said connection comprising (A) a first generally cylindrical inner conductor member,

(B) a second generally cylindrical inner conductor member (1) having a first axial end,

(2) connected at said first end to said first inner conductor member,

(3) having means forming a plurality of slots, each having a width (1), axially extending therein from said first end and forming a plurality of axially extending contact fingers, said fingers being circumferentially spaced apart by said slots and engaging said first inner conductor member at their inner surfaces,

(4) said second inner conductor member having a radius (r,,) to the outer surface of said fingers and having a radius (r to the inner surface of said fingers at said first end, and

(C) an outer conductor having a generally cyclindrical inner surface coaxial with and at least partly coextensive with the slots in said second inner conductor member and having an inner radius (R) related to the dimensions of said second inner conductor member by the following equation Z is the design value of the characteristic impedance between said outer conductor member and said inner conductor members at said slots, and

e is the net permittivity of the material between said outer conductor member and said slotted length of said second inner conductor member.

8. A coaxial transmission line connection consisting of a plug assembled with a jack, said connection comprising (A) a first inner conductor member (36) having a connecting part (36b) joined to a cylindrical part (36a) that has a first outer radius, (B) a second inner conductor member (14) having (1) a first end,

(2) a cylindrical part (14a) that has said first outer radius, I

(3) a generally-cylindrical slotted part (56, 57)

(a) joined with said cylindrical part thereof and extending therefrom to said first end, (b) having a plurality of fingers (56) axially extending to said first end and separated by slots (57) and telescopically receiving between them and frictionally engaging said connecting part of said first inner conductor member, (c) having said first radius to the outer surface of said fingers, and (C) a first outer conductor member (32) having a cylindrical inner bore coaxial with said first and second inner conductor members having (1) a first section (70) coextensive with said slotted part of said second inner conductor member and having a second inner radius, and

(2) a second section (68) contiguous with said first section thereof and at least partly coextensive with said cylindrical part of said first inner conductor member and having a third inner radius larger than said second radius.

' 9. A connection according to claim 8 further comprising (A) a second outer conductor member (16) having a cylindrical inner bore (1) coaxial with said first and second inner conductor members, and

(2) having a first section (58) (a) at least partly coextensive with said cylindrical part 14a) of said second inner conductor member, and

(b) having a radius equal to said third inner radius. 10. A connection according to claim 9 in which (A) said cylindrical inner bore of said second outer conductor member has a second section (60) (1) axially contiquous with said first section thereof and being closer than said first section to said first end of said second inner conductor member,

(2) around said cylindrical part of said second inner conductor member, and

(3) having a fourth inner radius less than said third radius,

(B) a cylindrical insulating sleeve (18) (1) disposed between said second inner conductor member and said second outer conductor member and at least coextensive with said first and second sections of said second outer conductor member,

where (2) having an inner radius substantially equal to said first radius,

(3) having an outer radius substantially equal to said third radius along the length thereof c0- extensive with said first section of said second outer conductor member, and

(4) having an outer radius less than said fourth radius along the length thereof coextensive with said second section of said second outer conductor member.

11. A connection according to claim 12 in which (A) said cylindrical inner bore of said first outer conductor member has a third section (72) (1) axially extending from and contiguous with the end of said first section thereof remote from said second section thereof, and

(2) having a fifth inner radius intermediate said second and third radii, and

(B) a hollow, cylindrical insulating sleeve (34) is (1) between and coaxial with said first outer conductor member and both said slotted part of said second inner conductor member and said cylindrical part of said first inner conductor member, and

12 (2) absent from the space within said third section of said first outer conductor member, and (C) means forming an annular air gap is provided between said first outer conductor member and the inner conductor member coextensive therewith over th entire axial length of said third section of said first outer conductor member.

References Cited UNITED STATES PATENTS 3,022,482 2/1962 Waterfield 333-97 3,245,027 4/1966 Ziegler 333-97 3,295,076 12/1966 Kraus 174-752 3,323,083 5/1967 Ziegler 333-97 3,350,666 10/1967 Ziegler 333-97 FOREIGN PATENTS 637,579 3/1962 Canada.

L. ALLAHUT, Assistant Examiner US. Cl. X.R. 

